The invention relates to a method for manufacturing an insulating bar for composite profiles, wherein the insulating bar is made from a thermoplastic plastics material and has a strip-like base body and, integrally formed on the opposite longitudinal edges thereof, connection strips.
Insulating bars of this kind are used during the manufacture of composite profiles for a shear-resistant mechanical connection and thermal insulation of metal profiles that are to be arranged on the outside and the inside, as are used in particular for manufacturing window frames, doorframes, façade elements and similar.
Insulating bars of this kind are known in many forms, for example among others from DE 32 36 357 A1, and depending on the spacing required between the metal profiles of the composite profile are made to appropriate widths.
Conventionally, the insulating bars have a substantially planar base body and are manufactured together with the connection strips in the course of extrusion, by means of a tool that is adapted to the cross sectional geometry.
More recently, it has been proposed to use insulating bars having a structured base body in order to improve the heat insulation without reducing the static strength of the composite profile (cf. for example EP 2 497 888 A2).
For improving the heat insulating properties of the composite profiles that are formed in this way, it has been proposed, among others in EP 2 497 888 A2, that the base body should be provided with a corrugated structure extending transversely as seen in the longitudinal direction of the insulating bar. The improvement in heat insulation that is achievable thereby results on the one hand from the fact that the corrugated structure increases the length of the path that the insulating bar provides for heat conduction from one metal profile to the other. On the other hand, the corrugated structure improves the rigidity of the insulating bar such that, with the same mechanical properties, smaller wall thicknesses are possible in the base body of the insulating bar, such that the cross section available in the insulating bar for heat conduction can additionally be reduced.
Moreover, losses due to both heat radiation and heat convection are expected to be lower as a result of using insulating bars of this kind.
In principle, this kind of insulating bar can be formed by machining out of an insulating bar that is manufactured with a substantially planar base body, or indeed can in principle be manufactured with the final structure by the method of injection moulding.
However, machining is not only time-consuming but also demands a high consumption of materials. The method of injection moulding, on the other hand, finds its limits very quickly, since the insulating bars are conventionally manufactured by the meter, for example to a length of 6 m. The injection moulds needed for this are not only extremely expensive but are also problematic, at the required insulating bar lengths, as regards sufficiently uniform filling of the moulds.
Further, a combined method based on injection moulding and extrusion is known (WO 2007/128787 A1) by means of which profiled elongate component parts can be made. With the method described there, it proves disadvantageous that the moulds that are needed for application to products described in this application require a very great longitudinal extent and are thus complex and disproportionately expensive. Admittedly, the structures described could be produced by this method in theory, but only with additional work steps that demand forming subsequent to the procedure of filling the mould during cooling of the product, or machining.